1. Field of the Invention
The invention relates generally to the coexistence of a plurality of wireless communications modules, and more particularly, to systems and methods for the coexistence schemes for a plurality of co-located wireless communications modules in a wireless communications device.
2. Description of the Related Art
To an increasing extent, a multitude of communication functions are being merged into mobile devices. As shown in FIG. 1, a cellular phone may connect to a wireless local area network (WLAN) via a WLAN module thereof and simultaneously communicate with a Bluetooth (BT) handset (or a Bluetooth car audio, or others) through a Bluetooth module thereof. A WLAN system is typically implemented inside buildings as an extension to wired local area networks (LANs) and is able to provide the last few meters of connectivity between a wired network and mobile or fixed devices. According to the IEEE 802.11 standard, most WLAN systems may operate in the 2.4 GHz license-free frequency band and have very low throughput rates because of coexistence interference from BT systems. Referring to FIG. 1, a WLAN is established by an access point (AP) connecting to a LAN by an Ethernet cable. The AP typically receives, buffers, and transmits data between the WLAN and the wired network infrastructure. The AP may support, on average, twenty devices and have a coverage varying from 20 meters in an area with obstacles (walls, stairways, elevators etc) to 100 meters in an area with clear line of sight. BT is an open wireless protocol for exchanging data over short distances from fixed and mobile devices, creating personal area networks (PANs). The cellular phone may receive voice over internet protocol (VoIP) data via the WiFi module and further transmit the VoIP data through an established PAN to the BT handset, and vice versa. Alternatively, the cellular phone may transmit digital music through the established PAN to be played back in the BT handset. The WLAN and BT systems both occupy a section of the 2.4 GHz Industrial, Scientific, and Medical (ISM) band, which is 83 MHz-wide. Due to cost issues as well as space requirements for components, modern electronic devices, such as cellular phones, Ultra-Mobile PCs (UMPCs) or others, are equipped with WLAN and BT modules sharing a single antenna instead of multiple antennas.
As an example shows in FIG. 2, a BT system uses a Frequency Hopping Spread Spectrum (FHSS) and hops between 79 different 1 MHz-wide channels in a Bluetooth spectrum. A WLAN system carrier remains centered on one channel, which is overlapped with Bluetooth spectrum. When the WLAN module and the Bluetooth module are operating simultaneously in the same area, as shown in FIG. 1, and a BT transmission occurs on a frequency band that falls within the frequency space occupied by an ongoing WLAN transmission, a certain level of interference may occur, depending on the signal strength thereof. Due to the fact that the WLAN module and BT module share the same spectrum and also share a single antenna, preventing interference therebetween is required.
FIG. 3 is a schematic diagram illustrating operation conflicts occurring between WLAN and BT communication services sharing a single antenna. In FIG. 3, the shared single antenna is switched between WLAN and BT communication services in a given time slot for transceiving data. If the BT communication service carries audio data that requires real-time transmission, for example, Synchronous Connection-Oriented (SCO) packets, the BT communication service would have a higher priority over the WLAN communication service. In this case, when a WLAN transceiving process takes place at the same time as the real-time BT transceiving process, a time slot will be assigned to the BT transceiving process and the WLAN transceiving process will be blocked. As shown in FIG. 3, the WLAN receiving operation (Rx operation) 1 occurs in the time slot, while the BT communication service is idle. Therefore, the Rx operation 1 is performed without interference and an acknowledgement (ACK) message 2 is sent to the WLAN AP (such as the AP in FIG. 1) as a reply message indicating that the Rx operation 1 has been completed. Following the Rx operation 1, another WLAN Rx operation 3 is performed. The Rx operation 3 is also performed without interference because the BT communication service is in the idle state. However, an ACK message 4 in response to the Rx operation 3 can not be replied to the WLAN AP, as its time slot has already been assigned to the Bluetooth transmitting operation (Tx operation). Accordingly, the Rx operation 3 would be determined to have failed. In response to the failure, the WLAN AP would re-transmit the data frame with a lower data rate in an attempt to successfully transmit data to the WLAN module of the mobile device. Unfavorably, the re-performed Rx operation 3 (denoted as 5), with a prolonged operation period, would be more likely to overlap with the BT transceiving process. Thus, data frame would once again be re-transmitted with an even lower data rate than that for the prior re-transmitted data, which would cause even more overlap with the BT transceiving process than the prior attempt. As a result, because the WLAN and BT wireless communication services sharing a single antenna are time-division accessed (i.e., only one communication service of WLAN and BT can be enabled at each time slot), throughput of the WLAN is greatly hindered.